Vegetation and hydrological monitoring by using satellite images has become an important research field. Both high temporal frequency and detailed spatial information are essential for an effective interpretation of satellite images. In particular, we focus on land surface temperature Tsurf, required for estimating evapotranspiration; this paper addresses the problem of computing spatial maps of Tsurf with a good spatial resolution and a high temporal frequency. For this purpose, we define a coupling process between {LANDSAT TM, NOAA/AVHRR} and DEM data